1. Field of the Invention
The present invention relates to an engine that burns an air-fuel mixture using secondary air and a vehicle including the same.
2. Description of the Related Art
Conventionally, engines using an internal EGR (Exhaust Gas Recirculation) technique have been developed (see JP 2002-174146 A, for example).
In the engine using the internal EGR technique, an exhaust gas in an exhaust port is taken into a cylinder in an intake stroke. This causes the oxygen concentration in the cylinder to be lowered to decrease a combustion temperature of an air-fuel mixture. As a result, heat loss of the engine can be minimized and NOx (nitrogen oxide) in the exhaust gas can be reduced. In addition, the exhaust gas is taken into the cylinder so that pumping loss of the engine can be decreased.
In the internal EGR technique, however, since the exhaust gas is taken into the cylinder as described above, the amounts of CO2 (carbon dioxide) and water vapor in the cylinder are increased. This causes combustion efficiency of the engine to be lowered, so that output characteristics of the engine cannot be sufficiently improved. Moreover, supply of the exhaust gas into the cylinder increases HC (hydrocarbon) and CO (carbon monoxide) in the cylinder, so that the exhaust gas cannot be sufficiently purified in some cases.